This weekend, the Bourne series returns to theaters, and we're all revisiting our memories of the original trilogy. Jason Bourne starts out as a man with very convenient amnesia — the kind that wipes out all your memories but leaves your ability to break out of an embassy intact. Could you really have a case of amnesia that erases your identity but leaves the skills in place?

Here's the weird real-life science of amnesia.

Discussing amnesia is a little like discussing cancer, in that it's hard to sum up because there are so many different causes and kinds. Basically, there are three types of amnesia — one that wipes out past memories, one that makes it impossible to make new memories, and one that does a little bit of both. All of these can last for an hour (or for life), happen with different degrees of severity, and can be the result of different things.

What Did Jason Bourne Actually Have?

In the films, Bourne clearly could make new memories, so he didn't have anterograde amnesia. It's possible that he had retrograde amnesia, which wipes out the past, but that tends to center around the traumatic event, allowing more distant memories in. Transient global amnesia takes out everything in the past, but tends to make it hard for a person to make new memories. All of these possible choices would have been caused by the bullet in his back and the ocean in his face. Most traumatic amnesia tends to be caused by injury to the brain, either through a stroke, a tumor, a seizure, an electric shock, drugs, inflammation, or oxygen deprivation. It seems, though, that Jason had a subtler injury.

More likely, Jason Bourne had God's Gift to Fiction Writers, known as hysterical or dissociative amnesia. This is a complete amnesia that leaves a person with a sense of self, but no memories of past events or connection to their current life. Occasionally they have trouble making new memories as well, and often engage in erratic behavior, but they do get the gradual recovery of past events the way that Bourne did.

Those who have seen the Bourne film noticed that Jason got a double shock — the trauma of a bullet wound and the shock of seeing that the murder of his potential victim was about to be witnessed by the victim's own child. If it was hysterical amnesia, the child did more to bring on the amnesia than the gunshot; this kind of amnesia is brought on by an emotional shock.

A real-life case of dissociative amnesia was brought on in a young soldier in basic training. Just after the stress and disorientation of training he found out that his girlfriend had disappeared with his car and all of his money. When he tracked her down he was guilted, because of her children's sickness and need for insurance, into considering marriage — and then promptly found out she had cheated on him. He drove away some distance, got out of the car, started walking, and was found by a gas station, disheveled and disoriented with no memory and no idea who he was.

While the man had no memories of himself or of any of the people in his life, he reported that he felt "worn out," and "sad," but didn't know why he felt those emotions. Many kinds of amnesia cause people to retain their emotional states, if more distantly than they otherwise would, without understanding their emotions. Over the next three weeks of hypnotherapy, the man regained most of his memories, and was eventually discharged.

Would He Retain His Abilities?

The major fascination with amnesia is that it's so specific. When an amnesiac wakes in a hospital, they may not know who they are or where they are, but they do know that they are in a hospital. They know what hospitals are and what they look like. They retain the ability to talk, to count, to recognize certain aspects of the world they live in, while blanking out personal memories entirely. One man, who realized one day as he was riding the subway that he didn't know who he was, amused his later acquaintances when he excitedly told them that he'd just discovered this great new band — called The Rolling Stones. Had they heard of it? The same man went to the ocean and dove in to see if he could swim. He was surrounded by Americans, but spoke with his native British accent. Some knowledge stayed. Some didn't.

What does the brain chuck overboard when it resorts to amnesia? Could someone with amnesia, say, suddenly realize they know their way around a gun, a conversation in German, and an ass-kicking?

We know that people who are unable to make new memories can learn procedural skills over time. People can also retain certain skills that they had before their injury. A brain infection once famously left a conductor with a memory span of ten seconds and no ability to recognize the people he had known before his infection, but he could still play the piano, and even conduct a choir. Both of these tasks take both physical and mental ability that he was able to produce at will, although he had no idea when he had gained that ability. Second language retention, or at least learning, is also possible.

One study, in which a anterograde amnesiac was taught French, showed that she apparently had the ability to learn it over time. We don't need personal memories to get skills — even skills that we acquire later in life. So it seems that Jason Bourne's retention of pen-fu despite amnesia could possibly be legit. But could his story about a government conspiracy be bogus? Could we take a look at the original movie, and consider Bourne an unreliable narrator?

Who Was the Real Villain of The Bourne Identity?

Say you happen to run a government agency tasked with taking out the most dangerous and brutal dictators and terrorists in the world. Of course, the morality of your agency is questionable, but you try make up for it by being very careful about what your agents do. They quietly, and without any collateral damage, kill the worst of the worst. Suddenly one agent goes missing. You assume he's been killed until you find him roughing up policemen and frightening embassy workers. Now you have a problem. You go after him and that problem is compounded when he starts making up stories about how your evil agency is grossly targeting the wrong people and acting as assassins for hire.

It very well could have happened. It's not that correct memories don't come back to dissociative amnesia patients. They almost always do. It's just that other things come back as well. Amnesia patients sometimes fill in the gaps with detailed false memories. It's called, and this is a great name, confabulary hyperamnesia.

A researcher doing a study in 2009 for Hôpital Saint Antoine asked a 68-year-old amnesia patient, "Do you remember what you did on March 13, 1985." He came up with a story about a visit to a forest with his family. When asked about the space program he predicted that we would soon land on the moon and see if it was habitable. Sometimes he misapplied what he did remember. Sometimes he remembered things that regularly happened, but attributed them to a specific date that was incorrect. Sometimes, like when talking about the moon landing, he simply went off the rails.

It would be natural to be freaked out by multiple passports and half-perceived memories of violence, of course. It would be easy to assume, and then "remember," the worst. In the first movie, could Jason Bourne have been the one in the wrong? Could he be making up a history for himself that didn't reflect reality? Later movies rather ruined the early ambiguity, but for that first one, we might very well have been watching a decent, if clandestine, agency desperately trying to take down a psychotic rogue spy. Now that would have been a fun movie to see — maybe it'll be that way in the remake.